/Engine/Source/Runtime/UMG/Public/Components/PanelWidget.h
Swaps the child widget out of the slot, and replaces it with the new child widget.
true if the CurrentChild was found and the swap occurred, otherwise false.
virtual bool ReplaceChild ( [UWidget](API\Runtime\UMG\Components\UWidget) * CurrentChild, [UWidget](API\Runtime\UMG\Components\UWidget) * NewChild )